I need a TAP, what do I need to know?
Deciding which TAP to purchase
Network TAPs (Test Access Points) are the absolute best way to gain access to network traffic, whether that be for network visibility solutions, network monitoring infrastructure, or network security auditing. It is common at a certain point in an organization’s growth for it to be recognized that mirror ports and SPAN (Switch Port ANalyzer) ports, due to their many limitations, are no longer sufficient to provide traffic to monitoring and or security tools. When it comes time to begin building a TAP infrastructure there are several details to consider. Some are simple and obvious, and others may be subtler and more nuanced. This article is intended to be a primer on the main points to consider when searching for Network TAPs for your environment. The information contained herein applies primarily to Cubro Network Visibility TAPs as these are the products I have the most first-hand knowledge of.
Media Type and Connector Type
The first consideration for which TAP is best suited to environment is a fairly obvious one: Which media type do you intend to tap? Really, this is the difference between an electrical connection or a fiberoptic connection. On the electrical side we generally are talking about UTP (or perhaps STP cabling; it makes no difference for our purposes), although the use of DAC (Direct Attach Cabling) is relatively common as well. Fiberoptic cabling can be broken down into Single-Mode and Multi-Mode fiber and Multi-Mode fiber presents two possible core diameters to choose from.
Each of these media types will in turn necessitate a connector type on the TAP as well; fiber, again, having the most options. First let’s address electrical connections and specifically UTP as it is the most common electrical media that a TAP will be used with. The category of UTP cabling doesn’t really impact the decision of which TAP we will choose but would, of course, impact supported speeds and cable length. The speed of the link is a differentiating factor though. Although it is not terribly common to encounter 10/100 links anymore it is important to point out that it is possible to have a completely passive electrical TAP (that requires power only for the monitor ports) at this speed. If you have 10/100 links in your environment the questions are whether it is more important to have a passive TAP that will not support 1G speeds or whether the option of upgrading the links without needing to replace the TAPs takes precedence.
10/100/1000 links are quite straightforward; you only have one choice. It is not possible to build a completely passive TAP for gigabit Ethernet over UTP; until now the industry approach has been to use relays to provide a fail-safe solution. This approach has not been problem-free though and instances where a link does not come back up or renegotiating a link after a failure takes an excessively long time are not rare. When I said you only had one choice earlier that is only partially true; in response to the number of issues with relay-based TAPs Cubro has designed a new type of 10/100/1000 TAP to drastically reduce these issues; adding a new, more reliable option to the mix.